This application for a Small Grant (R03) is from an independent investigator, who wishes to expand (but not change) her area of investigation to include neuroimaging of adolescents with bipolar disorder. The applicant is the principal investigator of an ongoing NIMH funded controlled longitudinal treatment study with bipolar adolescents "Treatment and Outcome of Early-Onset Bipolar Disorder" (1R01MH60845). There is ample support available to the PI to undertake neuroimaging studies in this population from experienced neuroimaging investigators at the North Shore-Long Island Jewish Health System. Neuroimaging studies have implicated white matter pathology in the neurobiology of bipolar disorder in the form of hyperintensities and functional abnormalities. In this pilot study we propose to use diffusion tensor imaging (DTI) to characterize possible abnormalities in the white matter connecting ventral brain regions that have been hypothesized to play a key role in the affective instability associated with bipolar disorder. Study participants will include 30 adolescents with Bipolar I disorder and 30 age, gender and IQ-matched healthy volunteers. Studies investigating the pathophysiology of bipolar disorder that involve this age group will include a greater number of first episode patients with a shorter duration of treatment. Recruitment for this proposed study will be facilitated by the PI's ongoing NIMH-funded longitudinal treatment study of bipolar adolescents.